Method and Apparatus for Variable Accuracy Inter-Picture Timing Specification for Digital Video Encoding

1. A method for decoding a plurality of video pictures of a video sequence, the method comprising: at a decoder, receiving a bitstream comprising an encoded first video picture and an encoded second video picture, wherein the encoded first video picture comprises at least one bidirectional predicted macroblock and the encoded second video picture comprises at least one unidirectional predicted macroblock that references the encoded first video picture and no bidirectional predicted macroblocks; and decoding the second video picture by using the first video picture as a reference.

2. The method of claim 1 , wherein decoding the second video picture comprises using a motion vector that references the first video picture.

3. The method of claim 2 further comprising receiving the motion vector for the second video picture from the bitstream.

4. The method of claim 2 further comprising computing the motion vector for the second video picture.

5. The method of claim 4 , wherein the motion vector for the second video picture is interpolated from a motion vector for a third video picture.

6. The method of claim 4 , wherein the motion vector for the second video picture is extrapolated from a motion vector for a third video picture.

7. The method of claim 1 , wherein the first video picture is a B video picture and the second video picture is a P video picture.

8. The method of claim 1 , wherein decoding the second video picture comprises decoding the unidirectional predicted macroblock by using a motion vector that references the first video picture.

9. An apparatus for decoding a plurality of video pictures of a video sequence, the apparatus to execute a process comprising: receiving a bitstream comprising an encoded first video picture and an encoded second video picture, wherein the encoded first video picture comprises at least one bidirectional predicted macroblock and the encoded second video picture comprises at least one unidirectional predicted macroblock that references the encoded first video picture and no bidirectional predicted macroblocks; and decoding the second video picture by using the first video picture as a reference.

10. The apparatus of claim 9 , wherein the decoding the second video picture comprises using a motion vector that references the first video picture.

11. The apparatus of claim 10 , wherein the process further comprising receiving the motion vector associated with the second video picture from the bitstream.

12. The apparatus of claim 10 , wherein the process further comprising computing the motion vector associated with the second video picture.

13. The apparatus of claim 12 , wherein the motion vector for the second video picture is interpolated from a motion vector for a third video picture.

14. The apparatus of claim 12 , wherein the motion vector for the second video picture is extrapolated from a motion vector for a third video picture.

15. The apparatus of claim 9 , wherein the first video picture is a B video picture and the second video picture is a P video picture.

16. The apparatus of claim 9 , wherein the first video picture is decoded before the second video picture.

17. The apparatus of claim 9 , wherein decoding the second video picture comprises decoding the unidirectional predicted macroblock by using a motion vector that references the first video picture.